Image processing device eliminating background noise

Abstract

An image processing device forming a reproduced image from a plurality of color recording signals, each of which is generated at a corresponding one of scans on an original image and derived from color digital signals obtained at the corresponding one of the scans, includes a threshold-value generation unit generating a threshold value based on the color digital signals at a first one of the scans, and a background removal unit reducing background noise in the reproduced image by using the threshold value at second and following ones of the scans.

What is claimed is: 
     
       1. An image processing device forming a reproduced image from a plurality of color recording signals, each of which is generated at a corresponding one of scans on an original image and derived from color digital signals obtained at said corresponding one of said scans, said image processing device comprising: a threshold-value generation unit generating a threshold value taking into account image characteristics of an entire image of said original image, said threshold value being obtained based on said color digital signals at a first one of said scans which is not a prescan; and   a background removal unit reducing background noise in said reproduced image by employing different threshold operations between said first one of said scans and second and following ones of said scans, said threshold value taking into account image characteristics of an entire image of said original image being used at said second and following ones of said scans.   
     
     
       2. The image processing device as claimed in claim 1, wherein said color digital signals comprise an R (red component) digital signal, a G (green component) digital signal, and a B (blue component) digital signal, and said color recording signals comprise a K (black component) recording signal, a C (cyan component) recording signal, an M (magenta component) recording signal, and a Y (yellow component) recording signal, wherein said K recording signal is obtained at said first one of said scans. 
     
     
       3. The image processing device as claimed in claim 2, wherein said K recording signal includes no background noise, so that no threshold operation is employed at said first one of said scans. 
     
     
       4. The image processing device as claimed in claim 1, wherein a predetermined threshold value is used at a time of said first one of said scans to reduce said background noise. 
     
     
       5. The image processing device as claimed in claim 1, wherein a local threshold value is used at a time of said first one of said scans to reduce said background noise, said local threshold value being obtained locally from said original image and obtained in realtime as said first one of said scans progresses. 
     
     
       6. The image processing device as claimed in claim 1, wherein said threshold-value generation means further generates threshold values at said second and following ones of said scans, and threshold values generated prior to a given one of said scans are used at said given one of said scans. 
     
     
       7. An image processing device comprising: input means for reading an original image to produce digital image data;   picture/letter area detection means for detecting picture/letter areas each of which is either a picture area or a letter area;   target-area detection means, responsive to said picture/letter area detection means, for identifying portions of said digital image data which are placed between said picture/letter areas;   background-density detection means for detecting a background density of said digital image data by using said portions;   background removal means for eliminating background noise by using said background density; and   output means for generating a reproduced image in which said background noise is eliminated.   
     
     
       8. The image processing device as claimed in claim 7, further comprising: first memory means for storing one line of results of said target-area detection means, said results corresponding to pixels of one scan line of said digital image data; and   second memory means for storing said pixels of said one scan line,   wherein said target-area detection means takes out one pixel from said second memory means and decides whether said one pixel is placed between said picture/letter areas, by using some of said results stored in said first memory means and corresponding to said one pixel and pixels on both sides of said one pixel.   
     
     
       9. the image processing device as claimed in claim 7, wherein said input means comprises means for scanning said original image more than one time to produce said digital image data at each time of said scanning, in order for said output means to generate said reproduced image, and wherein said background density is detected at a first one of said scanning which is not a prescan, and is used at second and following ones of said scanning. 
     
     
       10. The image processing device as claimed in claim 9, wherein said background removal means comprises: comparison means for comparing said digital image data with said background density, which digital image data is in a linear relation with density; and   selection means for selecting zero when a density associated with said digital image data is smaller than said background density and for selecting said digital image data otherwise.   
     
     
       11. The image processing device as claimed in claim 9, further comprising: first means for carrying out a first color correction process on said digital image data; and   second means for carrying out a second color correction process on said digital image data based on selected color correction coefficients,   wherein said background removal means comprises: comparison means for comparing said digital image data with said background density, which digital image data is in a linear relation with density; and   selection means for selecting an output of said second means when a density associated with said digital image data is smaller than said background density and for selecting an output of said first means otherwise.     
     
     
       12. The image processing device as claimed in claim 9, wherein said background removal means comprises means for carrying out a level conversion process suitable for said output means to generate said reproduced image by using threshold values changeable in accordance with said background density, so that a predetermined number of output levels are assigned to densities exceeding said background density. 
     
     
       13. An image processing device comprising: input means for reading an original image to produce digital image data;   picture/letter area detection means for detecting picture/letter areas each of which is either a picture area or a letter area;   target-area detection means, responsive to said picture/letter area detection means, for identifying portions of said digital image data which are in proximity of said picture/letter areas;   background-density detection means for detecting a background density of said digital image data by using said portions;   background removal means for eliminating background noise by using said background density; and   output means for generating a reproduced image in which said background noise is eliminated.   
     
     
       14. The image processing device as claimed in claim 13, further comprising memory means for storing results of said target-area detection means, said results corresponding to a predetermined number of pixels preceding a given pixel in said digital image data, wherein said target-area detection means decides whether said given pixel is in said proximity, by using said results stored in said memory means. 
     
     
       15. The image processing device as claimed in claim 13, wherein said input means comprises means for scanning said original image more than one time to produce said digital image data at each time of said scanning, in order for said output means to generate said reproduced image, and wherein said background density is detected at a first one of said scanning which is not a prescan, and is used at second and following ones of said scanning. 
     
     
       16. The image processing device as claimed in claim 15, wherein said background removal means comprises: comparison means for comparing said digital image data with said background density, which digital image data is in a linear relation with density; and   selection means for selecting zero when a density associated with said digital image data is smaller than said background density and for selecting said digital image data otherwise.   
     
     
       17. The image processing device as claimed in claim 15, further comprising: first means for carrying out a first color correction process on said digital image data; and   second means for carrying out a second color correction process on said digital image data based on selected color correction coefficients,   wherein said background removal means comprises: comparison means for comparing said digital image data with said background density, which digital image data is in a linear relation with density; and   selection means for selecting an output of said second means when a density associated with said digital image data is smaller than said background density and for selecting an output of said first means otherwise.     
     
     
       18. The image processing device as claimed in claim 15, wherein said background removal means comprises means for carrying out a level conversion process suitable for said output means to generate said reproduced image by using threshold values changeable in accordance with said background density, so that a predetermined number of output levels are assigned to densities exceeding said background density.